Epoxy resin based systems are widely used as sealing materials, coating compositions, adhesives, etc, in a variety of fields such as electricity, electronics, and civil engineering and construction, because, when cured, they exhibit excellent electrical insulating properties, are moisture proof, heat resistant, soldering resistant, chemical resistant, durable, have excellent adhesive properties and mechanical strength.
Two part epoxy resin based systems generally include a curable epoxy resin and a curing agent for the epoxy resin. As typical representative examples of curing agents, there are, for example, diethylenetriamine, triethylenetetramine, isophoronediamine, diaminodiphenylmethane, diaminodiphenylsulfone, polyamides, dicyandiamide, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methyl nadic anhydride, tertiary amines, imidazoles, and amine complexes of boron trifluoride. During preparation, both the epoxy resin and curing agent are generally dispersed or dissolved in a solvent, for example, an organic solvent, to reduce viscosity. Significant environmental concerns are created due to the use of such solvent-based systems since they create the potential for environmental pollution and health hazards.
Numerous curing agents dissolved or emulsified in water which may be used to cure epoxy resins have been developed to address environmental and health concerns. For example:
U.S. Pat. No. 4,197,389 discloses a curing agent prepared by reacting at least one polyepoxide compound with at least one polyalkylene polyether polyol to form an adduct which is subsequently reacted with a polyamine;
U.S. Pat. No. 5,246,984 teaches a two-component water based epoxy coating composition comprising an aqueous dispersion of a blend of a water-compatible polyamine-epoxy adduct prepared by reacting a monoepoxide and polyepoxide with a polyamine and a resin-compatible polyamine epoxy adduct prepared by reacting a monoepoxide with an aliphatic or cycloaliphatic polyamine;
U.S. Pat. Nos. 5,032,629 and 5,489,630 describe water compatible polyamine-epoxy adducts prepared by reacting poly(alkylene oxide) mono- or diamines with a polyepoxide to form intermediates which are then subsequently reacted with an excess of a polyamine;
U.S. Pat. No. 6,013,757 discloses waterborne polyamide curing agents produced from the reaction of long-chain dicarboxylic acids and aminoalkylpiperazines;
U.S. Pat. No. 6,245,835 describes amino-epoxy adduct curing agents prepared by reacting a polyoxyalkylenediamine with a polyepoxide and polyoxyalkylene glycol diglycidyl ether and emulsifying the reaction product in water;
U.S. Pat. No. 6,653,369 teaches a water dilutable amine curing agent which includes: an adduct obtained by a two-stage reaction of a polyepoxide with an amine; and an emulsifier obtained from the reaction of polyepoxides with chain extenders; and
U.S. Pat. No. 7,615,584 discloses a curing agent formed by blending a reaction product of a polyamine and aqueous epoxy resin with an amine-functional curing agent.
Some problems in using conventional solvent-free curing agents include: they exhibit a less than desirable viscosity making them difficult to apply and process; they are unable to properly wet the substrates to form continuous coatings or adhere to the surface of the substrates to which they are applied; they exhibit a short pot life when mixed with an epoxy resin; or are difficult to manufacture. It is an object of the present invention to provide a novel low VOC curing agent for use with aqueous epoxy resin compositions, which overcomes these problems as well as any problems arising from odor, toxicity and/or inflammability caused by the use of solvents, can be easily manufactured, and exhibits both low viscosity at high solids content and improved pot life.